Method and apparatus for measuring yarn tension

ABSTRACT

A method and apparatus for measuring yarn tension during highspeed transport of the yarn. The method involves engaging the running yarn with a pair of coupled torque-imparting rollers or similar yarn-contacting surfaces and electrically measuring the resulting torque which is proportional to the yarn tension. The apparatus is a torsion bar assembly with the two yarn-engaging rollers radially mounted on an arm connected by an axle to one end of the torsion bar with means to electrically measure the torque of the torsion bar produced by the yarn tension while the other end of the torsion bar is held in a fixed position by any suitable means.

United States Patent Rohner et al.

[ 1 July 25,1972

[54] METHOD AND APPARATUS FOR MEASURING YARN TENSION [72] Inventors: Dieter Rohner, I-lausen; Wolfgang Duhrlng, Erlenbach, both of Germany 3,203,235 8/1965 Stein ..73/144 FOREIGN PATENTS OR APPLICATIONS 118,336 5/1958 U.S.S.R. ..73/144 155,019 11/1963 U.S.S.R. ..73/144 Primary Examiner-Charles A. Ruehl Attorney-Johnston, Root, O'Keeffe, Keil, Thompson & Shurtlefi' [57] ABSTRACT A method and apparatus for measuring yarn tension during high-speed transport of the yarn. The method involves engaging the running yarn with a pair of coupled torque-imparting rollers or similar yam-contacting surfaces and electrically measuring the resulting torque which is proportional to the yarn tension. The apparatus is a torsion bar assembly with the two yarn-engaging rollers radially mounted on an arm connected by an axle to one end of the torsion bar with means to electrically measure the torque of the torsion bar produced by the yarn tension while the other end of the torsion bar is held in a fixed position by any suitable means.

10 Claims, 5 Drawing Figures PATENTEUJULZB I912 SHEET of 2 3.679.808

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ZKrsmdJ) G 1 6,. W m I I W R R H w WH 06 RN m EF TL E0 DW METHOD AND APPARATUS FOR MEASURING YARN TENSION The measurement of the tension on transported yarns, threads, cables, filaments and the like represents an extremely important problem for the fiber or filament producer and also for the textile processer. The tension is that component of force which acts on the running yarn in its direction of travel, i.e., along its length, this tension usually being measured in grams (force). In place of the total tensional force, the specific tension or unit stress is sometimes given, i.e., the force per unit of cross-sectional area. In the textile industry, it has been the usual practice to give the tension in grams/denier or grams/dtex, i.e., the force per unit of yarn size.

It will be understood that the term yarn" is employed herein in its most general meaning so as to include threads, monofilaments, tows, strands, cables or the like as employed in a wide variety of textile operations or in the initial production of natural, artificial or synthetic filaments and fibers.

In any operation in which a few or many yarn processing stages must be adjusted to one another, it is especially important to be able to measure and to adjust the tensional force on the yarn as accurately as possible and in a simple manner, so that disturbances or fluctuations will not occur in the course of production. Since the speed at which a yarn moves ahead or is transported from one point to another depends on the tensional force acting on it, it will be apparent that with a diminishing tensional force in a particular segment of the yarn path, the delivery speed of the yarn becomes lower so as to cause a bottleneck behind the point of reduced tension. Also, an undesirable and sometimes dangerous sagging of the yarn can occur at the point of reduced tension.

On the other hand, excessively high tensional forces and, accordingly, excessively high delivery speeds can lead to an undesirable thread or yarn accumulation. Devices which serve as a reservoir and can take up or give off a certain amount of yarn as required are rather costly and represent only a makeshift expedient. If at all possible, such devices must be avoided.

When the tensional force exceeds certain maximum values, a permanent deformation of the threads, filaments or yarns can occur whereby the properties of the yarn material itself is changed and a product is obtained which has substantial fluctuations in quality. At very high tensions, there is also the danger of thread breakage or a tearing or snapping of the filaments. For the above-mentioned reasons, it is therefore necessary to transport the yarn so that it runs under a yarn tension which is as constant as possible.

It is a known practice as disclosed in British Pat. No. 321,924 to measure the tension of a running yarn by means of a device in which the thread or yarn runs over two spaced rollers attached to a plate containing a third roller mounted on a spring-urged bar or similar support, the thread or yarn being looped under this third roller which together with the supporting bar is movable on a line between the first two rollers. As the tensional force increases, the running loop of yarn causes the third roller and its supporting bar to move against the force of a spring toward the paired rollers. A pointer associated with the third roller or its support indicates the tensional force of the yarn on a graduated scale. This method of measuring yarn tension is not very accurate, the indication being very sluggish or slow in its response to changes in yarn tension. Moreover, this apparatus and method is useless in the case of high linear velocities and high deniers (yarn size) of the threads or yarns being measured.

The methods of measuring yarn tension have been modified and improved and it is now more common to employ electronic thread tension meters (see Textil-Praxis 1961, No. 9, pages 90691l). in this instance, the thread or yarn is conducted around three rollers or three bars as in British Pat. No. 321,924, the measuring head being constructed as a capacitive differential indicator supplied with high frequency wherein the measured values are converted into electric voltages and fed to an indicating or registering device. The measuring sensitivity is thereby appreciably increased. However,

this type of method or device is not suitable for high deniers and high yarn tensions.

It is further known from British Pat. No. 730,035 that the thread or yarn can be conducted over one or two rollers which are fastened to a pivotable lever constructed as pointer, the yarn tension causing an indicated change in position of the pivoted lever against the action of a spring. This apparatus, however, is suitable only for threads or yarns of relatively low denier or strength and fails to operate properly when used to measure the tension of yarns of higher denier as well as yarns being conducted at high velocities.

One object of the present invention is to provide a method and apparatus for measuring the tension of a transported yarn whereby the measurement can be accomplished in a highly improved manner directly on the running yarn as it extends in a normally linear path between two points of practically any textile operation. Another object of the invention is to permit an accurate measurement of the tension of a yarn being transported at very high speeds and/or under very high tension, especially in operations requiring a high denier yarn. Still another object of the invention is to provide a tension measuring device which can be quickly engaged or disengaged from the yarn and which can be positioned temporarily by hand, if desired. Yet another object is to provide a relatively simply constructed apparatus for measuring the tension of transported yarns, preferably so as to be quite portable as well as being readily adapted for insertion in any yarn processing operation. These and other objects and advantages of the invention are discussed in greater detail hereinafter.

it has now been found, in accordance with the invention, that the measurement of tension of a rapidly transported yarn can be accomplished in an especially desirable manner and with good results by a method which comprises engaging the yarn during its transport with a coupled pair of torque-imparting yarn-contacting surfaces such that the yarn is directed from its normally linear path into a shallow S-curve path over one of said yarn-contacting surfaces and under the other of said yarn-contacting surfaces, mechanically transmitting the yarn tension exerted on said yarn-contacting surfaces to a torsion bar as a torque applied to said bar, and electrically measuring the resulting torque in said torsion bar with a wire strain gauge connected to said torsion bar so as to convert changes in the amount of applied torque into correspondingly proportional changes in electrical resistance, calibrated to indicate the tension in said yarn.

The apparatus of the invention is easily constructed and includes an elongated torsion bar, two coupled yarn-engaging means having substantially parallel axes spaced equidistantly and parallel to the axis of said torsion bar on a radially positioned supporting arm, means to rigidly connect said supporting arm at its midpoint between said yarn-engaging means to one end of said torsion bar, means to rigidly hold the other end of said torsion bar in a substantially fixed position, and at least one wire strain gauge strip fastened to said torsion bar on a free portion of its circumference for measurement of the amount of torque imparted by the tension of a transported yarn in contact with said yarn-engaging means.

The invention is particularly useful for measuring the tension on a yarn traveling at relatively high speeds, especially where the yarn is transported at a linear velocity of above about 1,000 meters/minute, e.g., on the order of 1,500 to 2,000 meters/minute or even more. Above all, the invention makes it possible to determine great tensile forces, e.g., where the yarn during its transport is subjected to a tension of more than about 1,000 kilograms. In this connection, the invention is especially adapted to the measurement of yarn tension where the transported yarn has a total yarn size of more than approximately 1 million dtex, e.g., up to several million dtex. (In determining yarn size, it will be noted that dtex l0/9-den ier, the so-called tex" unit having become more widely accepted in this art with dtex l0-tex being numerically similar to denier.)

The method and apparatus of the invention will be more readily understood from the following detailed description taken in conjunction with the accompanying drawings in which:

FIG. 1 is a schematic illustration of the manner in which a transported yarn is engaged with the measuring device of the invention;

FIG. 2 is partly schematic top plan view of one embodiment of the apparatus according to the invention, a central portion being shown in cross-section;

FIG. 3 is a side elevational view of the apparatus shown in FIG. 2, certain portions being omitted, in order to illustrate an alternative and preferred support of yarn-engaging rollers at one end of the torsion bar assembly; and

FIGS. 4a and 4b are geometrical constructions which are provided to more clearly illustrate the relationship between yarn tension and the torque applied to the torsion bar assembly.

As shown in FIGS. 1 and 2, the yarn I running between points A and B, for example in the direction of the arrow in FIG. 2, can extend approximately horizontally as shown, i.e., such that its normal path extends in a straight line corresponding to the broken line Y. It will be understood, of course, that the normal path of the yarn can extend in directions other than the horizontal, depending upon the particular textile or yarn treatment operation, the points A and B merely representing those points at which the yarn is supported or engaged by other apparatus, for example yarn guides, rollers or the like. As the yarn travels between these two fixed points A and B, it is engaged by each of the two rollers 2 and 2 in such a manner that the yarn l winds about the roller pair in the form of a shallow S-curve. Thus, when the device of the invention is positioned for yarn engagement and measurement of yarn tension, the normally linear path Y is deflected as the yarn passes under the first roller 2 and then over the second roller 2'.

The rollers 2 and 2' are positioned on a supporting arm 3 which is rigidly connected to an axle 4 which contains a preferably cylindrical torsion bar 5. The S-winding can be achieved in a very simple manner by inserting the roller pair in proximity to the running yarn in such a way that one roller 2 is positioned above and the other roller 2 below the yarn path Y (see FIG. I with the initially inserted rollers shown in broken lines). Thereupon the torsion bar assembly or axle 4, to which there can be fastened a simple handle 7 at one end, is turned on its longitudinal axis that the running yarn comes into contact with the roller pair to form the shallow S-curve winding 1 as represented in FIG. I. The handle 7 can be hand held to maintain one end of the device in a fixed position or any other suitable holding means can be employed.

Obviously, it is also possible to install the measuring device of the invention in fixed position, for example as may be required for a stationary continuous metering operation. In this case, the yarn itself can be introduced or threaded onto the measuring device in such a way that the coupled rollers 2 and 2 are wound in the illustrated S-curve path I.

As particularly illustrated in FIG. 2, the rollers 2 and 2 are preferably rotatably mounted on. the supporting arm 3, it being desirable to reduce as much as possible the frictional forces generated by the yarn as it partially contacts the rollers over a short distance on their preferably cylindrical surfaces. However, where such frictional forces are negligible, the rollers can be replaced by fixed bars, pins or the like, although it is advantageous even in this case to provide a curved yarn contacting surface to avoid increasing the normal tension in the yarn by insertion of the measuring device itself, especially at very high transporting velocities.

The axes of the rollers 2, 2' or similar yarn-engaging members should be substantially parallel to each other and spaced equidistantly in a radial direction outwardly from the axis of the torsion bar assembly or axle 4. The supporting arm 3 is rigidly connected to the front axle member 4 at the midpoint between the rollers 2 and 2 so that these rollers essentially provide a coupled torque-imparting means with the S-wound yarn l transmitting the yarn tension onto both rollers in a substantially identical manner and in the same clockwise direction as viewed in FIG. I. (In this respect, it will be apparent that a Z-winding with counterclockwise torque is equally suitable and fully equivalent to the illustrated form of the invention.)

The rear axle member 4" is adapted to be held in a fixed position against the torque imparted by the yarn tension acting on the rollers 2 and 2'. Both front and rear axle members 4 and 4" are separated from each other along a common axis, and the preferably cylindrical torsion bar 5 joins these two halves of the axle together to complete the assembly. This torsion bar of predetermined dimensions is preferably embedded in each axle member 4' and 4", but can be otherwise suitably connected in a rigid manner such that only the torsion bar 5 is subjected to the torque imparted by the rollers 2, 2' in response to the yarn tension.

The torque occurring in the bar 5 is determined with the aid of at least one wire strain gauge measuring strip 6 which is electrically connected over lines 8 and 8' with any suitable measuring device, for example, a carrier-frequency measuring bridge or other conventional bridge circuits used for the accurate determination of changes in electrical resistance. The term wire strain gauge" is employed herein to refer to the entire measuring device of which the illustrated measuring strip 6 is the essential component permitting a detection of the amount of torque imparted to bar 5. By means of the wire strain gauge, which in itself functions in a well known manner, the extension of the measuring strip 6 and thereby the corresponding extension of the bar 5 is determined on the basis of the torque occurring in the bar. From the measured torque, there can easily be determined the tensional force of the yarn.

In order to be able to accurately measure the torque occurring in the axle 4, with the aid of wire strain gauge measuring strips, an elongated axle having a large diameter is best interrupted in the middle and divided into two halves which are then connected with a bolt 5 of much smaller diameter as the torsion bar. This bolt carrying the measuring strip 6 at about its midpoint for detecting the torque is preferably surrounded over an intermediate portion by annular wall 9 or a suitable sleeve to protect the measuring strip from accidental damage or disconnection. It will be self-evident that preferably two measuring strips may be arranged in a bridge circuit for the elimination of interfering influences, e.g., at diametrically opposed positions on the bolt 5.

The bolt 5 as illustrated in FIG. 2 is a round bar which is made of a suitable material, preferably steel. The bolt should be constructed of a material of appropriate size and strength such that, on occurrence of the applied torque, it is strained to a maximum of 1 percent. The requisite strength can be easily calculated from the E-modulus of the material used for the bolt and the maximally occurring tensional forces to be exerted by the yarn in a given situation.

The temperature coefficients of the wire strain gauge measuring strips and the steel used for the bolt should be adapted to one another. The two halves of the axle 4,4 which are joined by the bolt 5 preferably consist of a material of poor heat-conducting properties, so that no heat is conducted from the point of measurement, i,e., the yarn contacting points, to the location of the wire strain gauge measuring strips. Accordingly, the two halves of the axle 4 and 4' are preferably composed of hard rubber or a similar rigid material which can also act as a heat insulator.

The rollers 2 and 2 about which the cable runs with a shal- I low S-shaped winding can be rotatably borne or mounted only at one end as represented in FIG. 2. However, it is also possible to rotatably mount these rollers at both ends as represented schematically in FIG. 3, which corresponds to a special embodiment of the invention. The second bearing point 10 of the roller 2 can be provided by an axially extended bow or U-shaped member 11 which is mounted on the side opposite to the yarn-contacting or yarn engaging side of the roller 2. Only one of the rollers 2 is shown in FIG. 3, the yarn in this case running in contact with the bottom surface of this roller. The second bow or added roller mounting member 11 for the other roller 2' is indicated in broken lines and should lie below since the yarn passes over the top surface of roller 2. With the use of bars or pins instead of rollers, the fastening to the supporting plate 3, whether rotatable or non-rotatable, can in an analogous manner be at one or both ends. A rotatable bearing or supporting means at both ends is especially preferred in the measuring of the tensional force of very heavy yarns, threads, strands or the like.

The geometric relationships presented by the device of the invention are illustrated in FIGS. 4a and 4b. With equilibrium conditions, i.e., when there prevails an equilibrium between the torque M appearing in the torsion bar and the linear force K of the yarn tension, one can readily derive the relationship:

FIG. 4a represents a purely arbitrary position of the two rollers in order to clearly show that the tension K is exerted in a direction perpendicular to the small radius R of the roller. On the assumption that the measurement is carried out at equal distance from the points A and B and the angle 0=0, which is the case when the roller pair has the position represented in FIG. 1 and as suggested by the geometric construction of FIG. 4b, there can be derived the relationships:

Suitable strain gauge measuring strips which can be used for purposes of the invention are conventional resistance elements in a strip of a length of approximately 3 to mm. These measuring strips operate on the principal that changes their electrical resistance are dependent on the amount of mechanical stress or strain, i.e., the tension, expansion or extension, imparted thereto. Such wire strain gauge measuring strips can be constructed in such a way that a resistance wire, metal film or semiconductor is embedded in a carrier of paper, synthetic resin, metal of the like. The measuring strip containing the resistance element, referred to as the wire, is then cemented to the measuring location of the torsion bar and participates in the change of length of the supporting surface to which it is secured. The resistance change is proportional to the change of length and is measured with a suitable bridge circuit, e.g., as in the well-known Wheatstone bridge. The length change occurring through temperature variation is compensated, for example, by a second measuring strip lying transversely to the direction of expansion or extension, this second strip forming a part of the bridge circuit in known manner. Further details in regard to wire strain gauge measur ing strips and their use may be found, for example, in the brochure Die DMS-Technik of the firm of Hottinger Baldwin Messtechnik GmbH, Darmstadt.

It is possible, especially in the case of a stationary continu ous metering of the yarn tension, to provide the coupled rollers, bars or pins on the side opposite the bracket 3 with a housing which is closed when the yarn runs between the rollers in measuring position. The yarn is thereby prevented from completely or partially working its way out of the measuring device due to lateral deflections of the thread or yarn path. The housing can consist, for example, of a simple cover plate which is fastened to the roller axles or to the framework of the machine on which the yarn is being drawn or transported. These and other minor variations can be readily employed within the scope of the invention.

The calibration of the measuring device is carried out in the following manner. Over two stationary deflection rollers or pins corresponding to points A and B and spaced at a distance of A,,, there is spanned a yarn or thread which is weighted on both sides of the stationary rollers with equal weights. The yarn or thread is then engaged with the rollers of the measuring device at the middle of the interval between the stationary rollers such that there is provided the S-shaped winding as represented in FIG. I. The torque occurring in the bolt or torsion bar of the axle 4 is then measured and calibrated with reference to the force known to be exerted on the yarn. This force on the yarn under these stationary conditions is yielded from the two weights with which the yarn is weighted.

The actual measuring takes place likewise as much as possible in the middle of the free cable interval. If the free yarn interval A differs from the interval A employed for the calibration, then the measuring results are to be multiplied by the factor where a, A and A correspond to the distances as shown in FIG. I.

In taking measurements, care must be taken that the midpoints of the measuring rollers 2,2 lie as closely as possible on the line along which the yarn ran before being engaged with the rollers, i.e., that the angle e (see FIG. 4a) is equal to zero.

With the method of the invention and with the apparatus according to the invention, the tensional force of a transported yarn can be very simply and accurately measured. By reason of the simple construction of the apparatus, which takes up a very small space and can be comfortably transported by one person, it is possible to measure yarn tension even where access to the yarn is rather difficult.

Since the measuring head is brought into its measuring position within a few seconds without difficulty and without neces sity of interrupting the running of the yarn, it is possible with the device according to the invention to rapidly check a relatively great number of yarn intervals. Even in places where a measuring with conventional devices would be too dangerous, for example because of the immediate proximity of entry rollers or reels, the yarn tension can still be measured both quickly and safely.

Where relatively large knots or snarls or the like occasionally exist in the yarn so as to raise the possibility that the yarn will drag along the measuring device or else break the yarn, then it is possible to pull the device off from the yarn within a split second. Thus, when held by hand, the measuring head can be immediately rotated out of position to avoid engagement with tangled or knotted yarns. When in a fixed or permanent position, yarn tension will not be accurately measured in these short tangled or knotted lengths, but the device can then be used to further meter the quality of the yarn, e.g., by providing a count of the number of times that tension is suddenly increased due to an imperfection in the yarn.

The invention is thus especially well suited for stationary continuous metering operation. It is very versatile for application to all types of yarn treating or handling operations. For example, with the aid of the permanently mounted or stationary device, one can carry out the measurement of the yarn tension in the stretching zone of a process for drawing yarn filaments or fibers, e.g., between two or more sets of feed and draw rolls. Other advantageous applications and uses for the invention will be readily suggested to those skilled in this art.

The invention is hereby claimed as follows:

I. A method of measuring the tension of a transported yarn which comprises:

aligning and engaging the yarn during its transport with a hand-held coupled pair of torque-imparting yarn-contacting surfaces such that the yarn is directed from its normally linear path into a shallow S-curve path over one of said yarn-contacting surfaces and under the other of said yarncontacting surfaces;

mechanically transmitting the yarn tension exerted on said yarn-contacting surfaces to a single torsion bar as a torque applied to said bar; and

electrically measuring the resulting torque in said torsion bar with a wire strain gauge connected to said torsion bar so as to convert changes in the amount of applied torque into correspondingly proportional changes in electrical resistance, calibrated to indicate the tension in said yarn.

2. A method as claimed in claim 1 in which the yarn is transported at a linear velocity above about 1,000 meters per minute.

3. A method as claimed in claim 1 in which the transported yarn is placed under a tension of more than about 1,000 kilograms.

4. A method as claimed in claim 3 in which the yarn has a total yarn size of at least 1 million dtex.

5. An apparatus for measuring the tension of a transported yarn which comprises:

a single elongated torsion bar;

two coupled yarn-engaging means having substantially parallel axes spaced equidistantly and parallel to the axis of said torsion bar on a radially positioned supporting arm;

means to rigidly connect said supporting arm at its midpoint between said yarn-engaging means to one end of said torsion bar;

means to rigidly hand-hold the other end of said torsion bar in a substantially fixed position; and

at least one wire strain gauge strip fastened to said torsion bar on a free portion of its circumference for measurement of the amount of torque imparted by the tension of a transported yarn in contact with said yarn-engaging means.

6. An apparatus as claimed in claim 5 wherein said torsion bar is composed of steel.

7. An apparatus as claimed in claim 5 wherein two coupled rollers as yarn-engaging means are rotatably mounted on said supporting arm.

8. An apparatus as claimed in claim 7 wherein each roller is rotatably supported at both ends by an arm including an axially extended member adjacent to each roller opposite the side of yarn engagement.

9 An apparatus as claimed in claim 5 wherein said means rigidly connecting and holding said torsion bar at either end consists of two axle members which are axially separated and joined solely by said torsion bar.

10. An apparatus as claimed in claim 9 wherein the axle member corresponding to said means rigidly holding said torsion bar in a substantially fixed position is provided with handle means. 

1. A method of measuring the tension of a transported yarn which comprises: aligning and engaging the yarn during its transport with a handheld coupled pair of torque-imparting yarn-contacting surfaces such that the yarn is directed from its normally linear path into a shallow S-curve path over one of said yarn-contacting surfaces and under the other of said yarn-contacting surfaces; mechanically transmitting the yarn tension exerted on said yarncontacting surfaces to a single torsion bar as a torque applied to said bar; and electrically measuring the resulting torque in said torsion bar with a wire strain gauge connected to said torsion bar so as to convert changes in the amount of applied torque into correspondingly proportional changes in electrical resistance, calibrated to indicate the tension in said yarn.
 2. A method as claimed in claim 1 in which the yarn is transported at a linear velocity above about 1,000 meters per minute.
 3. A method as claimed in claim 1 in which the transported yarn is placed under a tension of more than about 1,000 kilograms.
 4. A method as claimed in claim 3 in which the yarn has a total yarn size of at least 1 million dtex.
 5. An apparatus for measuring the tension of a transported yarn which comprises: a single elongated torsion bar; two coupled yarn-engaging means having substantially parallel axes spaced equidistantly and parallel to the axis of said torsion bar on a radially positioned supporting arm; means to rigidly connect said supporting arm at its midpoint between said yarn-engaging means to one end of said torsion bar; means to rigidly hand-hold the other end of said torsion bar in a substantially fixed position; and at least one wire strain gauge strip fastened to said torsion bar on a free portion of its circumference for measurement of the amount of torque imparted by the tension of a transported yarn in contact with said yarn-engaging means.
 6. An apparatus as claimed in claim 5 wherein said torsion bar is composed of steel.
 7. An apparatus as claimed in claim 5 wherein two coupled rollers as yarn-engaging means are rotatably mounted on said supporting arm.
 8. An apparatus as claimed in claim 7 wherein each roller is rotatably supported at both ends by an arm including an axially extended member adjacent to each roller opposite the side of yarn engagement.
 9. An apparatus as claimed in claim 5 wherein said means rigidly connecting and holding said torsion bar at either end consists of two axle members which are axially separated and joined solely by said torsion bar.
 10. An apparatus as claimed in claim 9 wherein the axle member corresponding to said means rigidly holding said torsion bar in a substantially fixed position is provided with handle means. 